Instrumentation has recently evolved which can measure the extremely weak, time varying magnetic fields outside the human body. These magnetic fields have been shown to be generated by electrical sources within the human body.
Magnetic field information is often combined with measurements of the temporal and spatial variations in the electrical potentials on the body surface for additional information about the internal condition of the body. Because the magnetic and electric measurements generate a tremendous amount of data in a short period of time, it is desirable to reduce the data and present it in a form which is more familiar and useful to medical diagnosticians. To accomplish this, it is generally believed that a presentation of the sources which generate the measured fields and potentials is desirable. Therefore a procedure which computes the locations and conditions of the sources from the measured data is required.
The problem with computing source locations and conditions from the magnetic field and electric potential measurements, is that the measured information is insufficient to uniquely determine the sources. In other words, many different source distributions can give rise to a specific set of measurements. The difficulty created by this ambiguity is referred to as "the inverse problem". Therefore it is necessary to incorporate as much a-priori knowledge as possible into the calculation.
In addition to an accurate description of the source distribution, it is necessary to be able to show the spatial relationship between the current distribution and anatomical structures in the subject. While techniques for "data fusion" have been developed, there remain many problems with merging complex 3D data sets.